1. Field of the Invention
The present invention relates to a mobile communication terminal, and particularly, to an apparatus and a method for compensating transmission power in a mobile communication terminal.
2. Description of the Background Art
FIG. 1 is a sketch showing a transmission block included in a mobile terminal.
As shown therein, the transmission block comprises a modem 100 and a transmission end 200.
The modem 100 modulates a digital signal into an analog signal, and the transmission end 200 controls gain of the analog signal outputted from the modem 100 according to a gain control signal (AGC value) of the modem 100 and outputs it to an antenna.
The transmission end 200 comprises an automatic gain controller (AGC) 20 for controlling gain of the analog signal (IF signal) according to the AGC value, a first SAW filter 21 filtering the IF signal of which gain is controlled, a mixer 22 for converting the filtered IF signal into a radio-frequency (RF) signal, a second SAW filter 23 filtering the RF signal, an amplifier for amplifying the filtered RF signal to be a predetermined level, and a duplexer 25 for outputting the amplified RF signal to the antenna.
Transmitting operation of the conventional mobile terminal as above will be described as follows.
The modem 100 converts the digital signal into an IF signal, that is, an analog signal and outputs the signal to the transmission end 200, and the AGC 20 of the transmission end 200 controls the gain of the IF signal according to the outputted AGC value.
The IF signal of which the gain is controlled is filtered in the first SAW filter 21, and after that, is converted into the RF signal. In addition, the RF signal is filtered in the second SAW filter 23, and is amplified in the amplifier to be a predetermined level. Therefore, the amplified RF signal is transmitted to a receiver via the duplexer 25 and the antenna (ANT).
Generally, the transmission block of the mobile terminal comprises passive components such as the first and the second SAW filters, and therefore, transmission power levels of the RF signals outputted from the transmission end by channels are differentiated by ripple characteristics of the passive components. Therefore, the modem 100 performs power calibration process for compensating the changes of power level on the transmission end by controlling the AGC 20 using a software.
However, since the transmission end of an IMT-2000 terminal has 12 channels and the respective channel has a plurality of power steps, it is actually impossible to perform the calibration processes for all power steps in all channels (12 channels) due to time limit.
Therefore, the modem 100 calculates AGC value differences of respective channels comparing to a reference channel for one power step in entire power section, and applies the corresponding AGC value to all power sections to perform the power calibration process.
Therefore, in the conventional art, the compensation values (AGC value) by respective channels are calculated for one power step, and the above compensation values are applied to remained power steps, and therefore, precise frequency compensation by respective channels and power levels can not be performed.